Additional Selenization Research Articles

Two-step approach for the growth of Cu0.5Ag0.5InSe2 thin films

In this work a facile two-step process, comprising of e-beam evaporated precursor deposition of (In/Cu/Ag/Se)× 3 multi-stack over substrate followed by additional selenization treatment, has been used to grow high-quality Cu0.5Ag0.5InSe2 (CAISe) films. The post selenization was performed at distinct temperatures in the range, 300 °C - 500 °C, and the effect of selenization temperature on the growth of CAISe thin films was reported in detail. The post selenization of (In/Cu/Ag/Se)×3 precursors at temperatures < 450 °C showed multiple spurious phases of Cu2Se, In2Se3, Ag2Se, and In6Se7 alongside CAISe. For selenization temperatures ≥ 450 °C, the films are purely polycrystalline, single-phase, and exhibiting tetragonal crystal structure with preferred (112) orientation belongs to CAISe. Further, Raman phase analysis for the precursors selenized at ≥ 450 °C displays intense phonon modes at 67 cm−1(B2), 171 cm−1 (A1), and 212 cm-1 (B2/E1) corresponding to single phase tetragonal CAISe. The compositional analysis of (In/Cu/Ag/Se)× 3 precursors selenized at 475°C indicated that the films are nearly stoichiometric with an average atomic composition of Cu+Ag = 25.69, In = 24.39, and Se = 49.92 in at. %. The elemental depth profile across thickness shows that the distribution of elements is uniform. The micrograph of precursor stack selenized at 475 °C found to have compact and larger grains (~1.0 µm). The optical studies of stacked precursors selenized between 450 °C and 500 °C reveal a solo absorption edge, with an optical band gap ranging between 1.13 eV and 1.05 eV. The stacked layers selenized at 475 °C exhibits higher hole mobility of 27.0 cm2/V-s, and a moderate concentration of 1.26 × 1016 cm−3.

Growth and structural characterization of Sb2Se3 solar cells with vertical Sb4Se6 ribbon alignment by RF magnetron sputtering

Sb2Se3, (ASe) thin-films were deposited as the absorber layers in photovoltaic solar cells using the radio frequency magnetron sputtering deposition technique. Starting from a binary target, high quality crystallization and good vertical alignment of Sb4Se6 ribbons were attained at growth temperatures below 300 °C, and use of an additional selenization process was unnecessary for compensating Se loss. By the structural characterization of films grown on different substrates, a strong dependence of the ribbon orientation on the substrate type was verified. This study clearly confirms that the ribbon alignment is the key factor for enhancing the performance of Sb2Se3 solar cells, in particular the short circuit current density (J sc). A photovoltaic efficiency of 0.24% and a J sc of 5 mA cm−2 were obtained by depositing ASe on Mo, in a CuInGaSe2-like solar cell structure (Al:ZnO/ZnO/CdS/ASe/Mo/Glass), while the J sc was boosted up to 27 mA cm−2 when the ASe solar cells were fabricated in superstrate configuration with an Au/ASe/CdS/FTO architecture, leading to an efficiency of 2.36%.

Effects of annealing atmosphere on the performance of Cu(InGa)Se2 films sputtered from quaternary targets.

Quaternary sputtering without additional selenization is a low-cost alternative method for the preparation of Cu(InGa)Se2 (CIGS) thin film for photovoltaics. However, without selenization, the device efficiency is much lower than that with selenization. To comprehensively examine this problem, we compared the morphologies, depth profiles, compositions, electrical properties and recombination mechanism of the absorbers fabricated with and without additional selenization. The results revealed that the amount of surface Se on CIGS films annealed in a Se-free atmosphere is less than that on CIGS films annealed in a Se-containing atmosphere. Additionally, the lower amount of surface Se reduced the carrier concentration, enhanced the resistivity of the CIGS film and allowed CIGS/CdS interface recombination to be the dominant recombination mechanism of CIGS device. The increase of interface recombination reduced the efficiency of the device annealed in a Se-free atmosphere.

Magnetron sputtering deposition and selenization of Sb2Se3 thin film for substrate Sb2Se3/CdS solar cells

Antimony triselenide (Sb2Se3) thin film was fabricated as the absorber layer in photovoltaic solar cell using magnetron sputtering deposition method. An additional selenization process was applied to increase the crystallinity of the film as well as to compensate for selenium loss during the sputtering process. Various analytical techniques were used to characterize the morphology and composition of the film. It was found that the annealing temperature is the key factor for thin film quality and the sample annealed at 350 °C shows the optimum result with a power conversion efficiency of 2.1%.

Comprehensive characterization of CIGS absorber layers grown by one-step sputtering process

We have demonstrated that the use of a one-step sputtering process allowed for the fabrication of copper indium gallium diselenide (CIGS) thin films by RF magnetron sputtering without an additional selenization process. The CIGS thin films deposited at different substrate temperatures were synthesized on soda-lime glass (SLG) substrates using a single quaternary CIGS target. The film composition ratios of ([Cu]/[In]+[Ga]), ([Ga]/[In]+[Ga]), and ([Se]/[Cu]+[In]+[Ga]) were almost consistent with those of the sputtering target. X-ray diffraction (XRD) and Raman results showed that the crystallinity of the CIGS thin films was gradually improved as substrate temperatures increased. Transmission electron microscopy (TEM) showed that the films grown at 600 °C have a columnar structure with the grain size of ~100 nm. In addition, for the CIGS films grown at 600 °C, TEM-EDX analysis revealed that the synchronized fluctuation of the Cu and Se signals was observed in the direction of the film depth, while the In and Ga signals were constant. As a result, the CIGS solar cell made using the film showed a degraded cell efficiency of 2.5%, which might be have been caused by not only Cu-rich and Se-poor compositions but the locally unstable composition in the CIGS films fabricated by one-step sputtering.

Quaternary Sputtered Cu(In,Ga)Se2Absorbers for Photovoltaics: A Review

Quaternary sputtering is a promising alternative to more established deposition methods for the fabrication of Cu(In,Ga)Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (CIGS) thin films for photovoltaics (PV). In this technique, a single sputtering target containing all four constituents is employed to deposit the CIGS film. Quaternary sputtering offers several advantages over other deposition methods, including excellent uniformity over large areas, high material usage, and less reliance on toxic Se precursors such as H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se. Despite these advantages, several drawbacks remain. To date, devices fabricated by quaternary sputtering without additional selenization have been limited in efficiency to about 11%, and realizing bandgap grading in order to match the performance of the best evaporated devices presents a challenge. We discuss the prospects for quaternary sputtering as a fabrication technique for CIGS and highlight areas of research that may result in improved performance. Target fabrication and usage is reviewed. We also present results for films and devices including data for the optical constants of sputtered CIGS. Some recent previously unpublished results, including a study of impurities in CIGS sputtering targets and the first demonstration of a CIGS device on a flexible glass substrate, are discussed

Study on the CIGS Thin Film Formation by Modified Spray Process

The highly uniform polycrystalline CuIn0.7Ga0.3Se2 (CIGS) thin films for solar cell application were successfully synthesized on the glass substrates using a modified spray process and a continuous flow micro-reactor (CFM) process at low temperature. The as-deposited thin films prepared by each method were annealed under vacuum condition without additional selenization. In order to study the influence of annealing temperature on the properties of the CIGS films, annealing temperature were varied from 200°C to 400°C. The annealing temperature exerted an effect on the properties of the prepared thin films. Based on the XRD measurements, the optimum annealing condition to synthesize the CIGS thin films was 200°C. The crystalline structure of the film annealed at 200°C was in good agreement with the tetragonal structure in the reference. CuIn0.7Ga0.3Se2 thin films were also deposited by a solution-based CFM method and were then thermally treated under the same conditions as the spray. They were compared with the properties of the films deposited by the spray in order to figure out which deposition method is more effective for the synthesis of the CIGS thin films. XRD, SEM, UV-vis, and XPS were employed to study the influence of annealing temperature on the physical properties of the films.

Selenization of Sb2Se3 absorber layer: An efficient step to improve device performance of CdS/Sb2Se3 solar cells

Sb2Se3 appeared as a very promising solar absorber because of their attractive material, optical and electrical properties. Previously, we reported thermal evaporated superstrate CdS/Sb2Se3 solar cell achieving 1.9% efficiency. In this letter, we improved device performance to 3.7% (Voc = 0.335 V, Jsc = 24.4 mA/cm2, and FF = 46.8%) by an additional selenization step. Careful external quantum efficiency, capacitance-voltage profiling, and photoresponse study indicated selenization probably compensated selenium loss during thermal evaporation, reducing VSe associated recombination loss and improving device performance.

Polycrystalline Cu(In, Ga)Se2 Thin Films and PV Devices Sputtered From a Binary Target without Additional Selenization

This work presents a novel method to form polycrystalline CuIn1−xGaxSe2 (CIGS) thin film by co-sputtering of In–Se and Cu–Ga alloy targets without an additional selenization process. An attempt was also made to thoroughly elucidate the surface morphology, crystalline phases, physical properties, and chemical properties of the CIGS films by using material analysis methods. Experimental results indicate that CIGS thin films featured densely packed grains and chalcopyrite phase peaks of (112), (220), (204), (312), and (116). Raman spectroscopy analysis revealed chalcopyrite CIGS phase with Raman shift at 175cm−1, while no signal at 258cm−1 indicated the exclusion of Cu2-xSe phase. Devices built with these films exhibit efficiencies as high as 8.6%.

A non-selenization technology by co-sputtering deposition for solar cell applications.

This work presents a novel method to form polycrystalline Cu(In(1-x)Ga(x))Se(2) (CIGS) thin film by co-sputtering of In─Se and Cu─Ga alloy targets without an additional selenization process. An attempt was also made to thoroughly elucidate the surface morphology, crystalline phases, physical properties, and chemical properties of the CIGS films by using material analysis methods. Experimental results indicate that CIGS thin films featured densely packed grains and chalcopyrite phase peaks of (112), (220), (204), (312), and (116). Raman spectroscopy analysis revealed chalcopyrite CIGS phase with Raman shift at 175 cm(-1), while no signal at 258 cm(-1) indicated the exclusion of Cu(2-x)Se phase. Hall effect measurements confirmed the polycrystalline Cu(In,Ga)Se2 thin film to be of p type semiconductor with a film resistivity and mobility of 2.19×10(2) Ω cm and 88 cm(2)/V s, respectively.

Polycrystalline Cu(In, Ga)Se2 Thin Films and PV Devices Sputtered from a Binary Target without Additional Selenization

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Cu(In,Ga)Se 2 thin films and devices sputtered from a single target without additional selenization

Typically, Cu(In,Ga)Se 2 (CIGS) thin films for photovoltaic devices are deposited by co-evaporation or, alternately, by deposition of the metals with or followed by treatment in a selenium environment. In this article, we describe CIGS films that are instead deposited by RF magnetron sputtering from a single quaternary target without any additional selenization. Devices built with these films exhibit efficiencies as high as 8.9%. We demonstrate that deposition power can be varied in order to change the film morphology and improve device performance.